The Akeeba Admin Tools is a great addition to securing your Joomla CMS. But there are some features that need some tweaking for running smoother. One of these is an admin's ability to change a user in the back-end.
The Admin Tools from AkeebaBackup is a very useful tool to install, but it is not set up for back-end editing of users and this can in some cases cause some problems to change the user from the Admin account.
When you install the Admin Tools it comes with the disable setting as default. This is however easy to change.
Admin Tools Professional contains a feature called Web Application Firewall. One of the security features applied by WAF is to block editing or adding Managers, Administrators, and Super Administrators.
Go to Components, Admin Tools, and click on the Web Application Firewall (WAF) button.
On the new page, click on the WAF Configuration. Find the Disable editing backend users' properties option and set it to No and Click Save & Close.
Now you can create and edit all users on your site. For security reasons, remember to re-enable this option after you're done adding/editing users!